The Met Office Unified Model Global Atmosphere 3.0/3.1 and JULES
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Geosci. Model Dev., 4, 919–941, 2011 www.geosci-model-dev.net/4/919/2011/ Geoscientific doi:10.5194/gmd-4-919-2011 Model Development © Author(s) 2011. CC Attribution 3.0 License. The Met Office Unified Model Global Atmosphere 3.0/3.1 and JULES Global Land 3.0/3.1 configurations D. N. Walters, M. J. Best, A. C. Bushell, D. Copsey, J. M. Edwards, P. D. Falloon, C. M. Harris, A. P. Lock, J. C. Manners, C. J. Morcrette, M. J. Roberts, R. A. Stratton, S. Webster, J. M. Wilkinson, M. R. Willett, I. A. Boutle, P. D. Earnshaw, P. G. Hill, C. MacLachlan, G. M. Martin, W. Moufouma-Okia, M. D. Palmer, J. C. Petch, G. G. Rooney, A. A. Scaife, and K. D. Williams Met Office, FitzRoy Road, Exeter, EX1 3PB, UK Received: 20 April 2011 – Published in Geosci. Model Dev. Discuss.: 17 June 2011 Revised: 26 September 2011 – Accepted: 14 October 2011 – Published: 26 October 2011 Abstract. We describe Global Atmosphere 3.0 (GA3.0): configurations (Cullen, 1993). For nearly twenty years, this a configuration of the Met Office Unified Model (MetUM) has provided the Met Office and its collaborators with the developed for use across climate research and weather pre- benefit of a single technical infrastructure, dynamical core diction activities. GA3.0 has been formulated by con- and collection of atmospheric parametrizations and has al- verging the development paths of the Met Office’s weather lowed them to develop modelling systems efficiently with- and climate global atmospheric model components such out the duplication of effort on common programming tasks. that wherever possible, atmospheric processes are modelled This technical efficiency also extends to the scientific devel- or parametrized seamlessly across spatial resolutions and opment of the model. Climate models are being run at ever timescales. This unified development process will provide higher resolution and applied to problems beyond the predic- the Met Office and its collaborators with regular releases of tion of mean climate states, such as the frequency and sever- a configuration that has been evaluated, and can hence be ap- ity of extreme weather events (Huntingford et al., 2003). This plied, over a variety of modelling regimes.´ We also describe requires the accurate modelling of mesoscale systems, which Global Land 3.0 (GL3.0): a configuration of the JULES com- has long been the remit of NWP forecasting. Conversely, to munity land surface model developed for use with GA3.0. consistently improve the quality of weather forecasts, global This paper provides a comprehensive technical and scien- and regional NWP models are starting to employ more com- tific description of the GA3.0 and GL3.0 (and related GA3.1 plexity and modelling elements of the Earth System that have and GL3.1) configurations and presents the results of some previously been the reserve of climate modelling, such as initial evaluations of their performance in various applica- atmospheric composition (Milton et al., 2008) and detailed tions. It is to be the first in a series of papers describing modelling of the water cycle (Balsamo et al., 2011). Collab- each subsequent Global Atmosphere release; this will pro- oration between climate and weather scientists and the use vide a single source of reference for established users and of a common atmospheric model aids users of the MetUM to developers as well as researchers requiring access to a cur- make these developments in an efficient manner. rent, but trusted, global MetUM setup. As well as the efficiency of central code development, us- ing the MetUM allows the Met Office to take advantage of the recognised synergies between climate and NWP mod- 1 Introduction elling (Martin et al., 2010; Senior et al., 2010). By study- The Met Office Unified Model™ (MetUM) is a highly flex- ing the same model formulation across a range of tempo- ible atmospheric model that was designed from its inception ral scales one can distinguish systematic biases that develop to be used for both climate research and Numerical Weather on very short timescales due to errors in rapidly responding Prediction (NWP) activities in both global and limited area parametrizations (e.g. clouds and precipitation) from those that develop due to more slowly evolving elements such as the soil moisture content in the land surface model. Study- Correspondence to: D. N. Walters ing the same model across different resolutions also allows (david.walters@metoffice.gov.uk) one to investigate the sensitivity of processes such as tropical Published by Copernicus Publications on behalf of the European Geosciences Union. 920 D. N. Walters et al.: MetUM GA3.0/3.1 and JULES GL3.0/3.1 configurations cyclone formation to the resolved spatial scales (Heming, longstanding differences from the climate model; we label 2010) and the efficiency of parametrization schemes in mod- these GA3.1 and GL3.1. These differences and a discussion elling unresolved processes such as atmospheric convec- of the motivations behind them are included in Sect. 5, Fi- tion (Lean et al., 2008). Finally, verifying a model against nally, we present some initial results from assessments of the observations, atmospheric analyses and climatologies greater configurations in Sect. 6 and summarise our current position exposes its deficiencies and leads to a more robust formula- in Sect. 7. tion. For this reason, the Met Office has kept the develop- ment paths of the global forecast models within its opera- 2 The “Global Atmosphere” configuration tional NWP suite and the Met Office Hadley Centre’s cli- 2.1 Definition of the Global Atmosphere mate and seasonal forecasting models roughly aligned. Ma- jor developments introduced in one set of models are usu- The principle of the Global Atmosphere configuration fol- ally adopted by the other after only a short delay (e.g. Martin lows that set out for the atmospheric component of the et al., 2006; Milton et al., 2005). This process is hampered, HadGEM3 family in Hewitt et al. (2011), but extended however, when developments that become well established to include short-range NWP configurations. The Global in one context prove deficient in another, which can lead to Atmosphere is a single choice of dynamical core, atmo- either the inefficient development of a more general solu- spheric parametrizations, and options therein, applied to tion or a divergence of the configurations. To improve this an atmospheric MetUM component which may well itself situation, the Met Office has recently formalised the coor- be part of a larger system. For example, the global cli- dination of these development paths by merging them into mate modelling system HadGEM3-AO currently uses a Me- a single “Global Atmosphere” configuration. This is a com- tUM Global Atmosphere component coupled internally to mon choice of scientific options that will be applied to all a JULES Global Land component and externally to the of the Met Office’s global atmospheric MetUM components. NEMO ocean model (Madec, 2008) and the Los Alamos sea A similar approach is planned for other components of the ice (CICE) model (Hunke and Lipscombe, 2008) via the OA- Earth System such as the land surface, ocean, sea-ice and SIS coupler (Valcke, 2006). The Met Office’s short-range atmospheric chemistry and aerosols. The combined Global NWP forecasting system currently uses the MetUM Global Atmosphere is a logical progression from the decision to de- Atmosphere and JULES Global Land initialised via a 4D-Var velop a single atmospheric formulation for use across the data assimilation cycle (Rawlins et al., 2007), a soil moisture Met Office Hadley Centre’s climate models: the HadGEM3 analysis system (Best and Maisey, 2002) and uses fixed sea- (Hadley Centre Global Environmental Model version 3) fam- surface temperature (SST) and sea ice fields from the OSTIA ily. In recognition of this, the atmospheric components of (Operational Sea-surface Temperature and sea Ice Analysis) the two operationally used climate modelling systems pre- system (Donlon et al., 2011). viously known as HadGEM3-r1.1 (Hewitt et al., 2011) and To illustrate the breadth of potential applications, the fol- HadGEM3-r4.0 (Arribas et al., 2011) have been labelled lowing is a list of operational or production systems in which GA1.0 and GA2.0, respectively. the Met Office is using or plans to use Global Atmosphere This paper describes the first such MetUM configuration configurations: developed for use in short-range NWP as well as climate modelling: Global Atmosphere 3.0 (GA3.0). It also de- – Deterministic NWP (6 days): atmosphere/land-only, scribes a configuration of the JULES (Joint UK Land En- started from 4D-Var data assimilation and soil mois- vironment Simulator, Best et al., 2011; Clark et al., 2011) ture, snow and SST analyses. Produces global weather land surface model developed for use with GA3.0; this is la- forecasts and boundary conditions for limited area NWP belled Global Land 3.0 (GL3.0). In the following section models; we describe precisely what we mean by the Global Atmo- – Ensemble prediction system (15 days): 24 members sphere configuration, the vision of how this could be used with stochastic physics parametrizations initialised by the Met Office and the wider MetUM community and our from perturbed deterministic analyses and using per- plans for a more open development process. Again, this is de- sisted SST anomalies (Bowler et al., 2008). Provides signed as a general template that could be followed for other probabilistic global weather forecasts and boundary Earth System components. In Sect. 3 we scientifically de- conditions for the regional ensemble; scribe both GA3.0 and GL3.0, whilst in Sect. 4 we provide a more detailed description of some of the major develop- – Monthly forecasting system (60 days): Lagged ments made since GA2.0 and its accompanying Global Land ensemble (28 members per week) of coupled Me- configuration GL2.0.